1.Field of the Invention
The present invention relates to an apparatus for collecting the fuel leaked from the fuel injection system of an internal combustion engine through clearances such as a the circumferential clearance of the needle valve, etc. of the fuel injection nozzle for injecting fuel into the cylinder to a leak oil collection pipe through the leak passage in said fuel injection nozzle. The apparatus is particularly applied to an internal combustion engine using low boiling point fuel such as DME(dimethyl ether), LPG(liquefied petroleum gas), etc.
2. Description of the related Art
In a diesel engine having a cylinder into which low boiling point fuel such as DME(dimethyl ether), LPG(liquefied petroleum gas), etc. pressurized into a liquid state, is injected from the injection nozzle the fuel is pressurized in the fuel supply system for supplying the fuel to the injection nozzle and in the fuel injection system, because the fuel must be injected into the cylinder in a liquid state.
Therefore, in the fuel injection system of such a diesel engine, the amount of leaked fuel leaked to the upper part of the fuel injection nozzle through clearances such as the circumferential clearance of the needle valve, etc. in a pressurized liquid state of low viscosity increases, so the leaked fuel is collected to be supplied for combustion, because if the leaked fuel is released into the atmosphere the thermal efficiency of the engine reduces.
Generally, the fuel leaked from the injection nozzle is collected to the fuel supply system to be reused as disclosed in Japanese Laid-Open patent Application No. 9-112732.
However, in the case of a diesel engine using low boiling point fuel, it is conceivable, as the fuel is pressurized in the fuel supply system, to introduce the leaked fuel to the intake air supply passage to be vaporized thereby and supplied into the cylinder together with the fresh air (intake air of the engine) as an air-fuel mixture, instead of returning the leak fuel from the injection nozzle to fuel supply system as is in the case of a diesel engine using light oil or heavy oil as described in said Japanese Laid-Open patent Application No. 9-112732.
When the leaked fuel from the injection nozzle is introduced into the air supply passage to be mixed with the fresh air to be supplied as intake air of the engine, the mixture is extremely lean mixture of the leaked fuel and fresh air, and incomplete combustion with unburned fuel remained is prone to occur in the cylinder.
Particularly, in a low load range with decreased injection amount of fuel into the cylinder, the combustion environment in the cylinder is such that the incomplete combustion of the lean mixture containing the leak fuel is liable to occur, and fuel consumption increases due to the incomplete combustion of the leaked fuel and at the same time the deterioration in exhaust emission is induced due to the generation of harmful matter such as CO(carbon monoxide) and HC(hydro carbon).